1. Field of the Invention
The present invention relates to a technical field of, for example, a controller that controls an electric motor system having a three-phase AC motor.
2. Description of Related Art
An example of a control method of driving a three-phase AC motor is pulse width modulation (PWM) control. The PWM control is to control a power converter (for example, an inverter) that converts a DC voltage (DC power) into an AC voltage (AC power) based on a magnitude relation between a phase voltage command signal, which is set from the viewpoint of matching phase currents supplied to a three-phase AC motor with a desired value, and a carrier signal of a predetermined frequency.
Another example of the control method of controlling a three-phase AC motor is rectangular wave control. The rectangular wave control is to control a power converter (for example, an inverter) that converts a DC voltage (DC power) into an AC voltage (AC power) based on a rectangular wave signal of which the phase has been adjusted from the viewpoint of matching a torque of a three-phase AC motor, which is estimated from phase currents supplied to the three-phase AC motor, with a target torque.
When a power converter is controlled, phase currents are generally detected by current sensors. Here, there is a possibility that a detection signal of a current sensor will include an error (for example, an offset error in which a signal obtained by adding a DC component to an actual current signal is output as a detection signal, or a gain error in which a signal obtained by amplifying or attenuating an actual current signal is output as a detection signal). Therefore, techniques of correcting an error included in a detection signal of a current sensor in order to improve detection accuracy of the current sensor have been proposed. For example, Japanese Patent Application Publication No. 2000-023490 (JP 2000-023490 A) discloses a technique of correcting an error while a PWM signal for operating an inverter is not output from a controller (that is, while a phase current does not flow and until charging of a capacitor is completed after an electric motor is started).
An example of a document of the related art is Japanese Patent Application Publication No. 2009-098091 (JP 2009-098091 A).